1. Field of the Invention
The invention relates to an actuator module with a piezoelectric actuator having a sheath, which can be used for instance in a piezoelectric injector for chronologically and quantitatively precise metering o fuel in an internal combustion engine.
2. Description of the Prior Art
One such piezoelectric injector essentially comprises a holder body and the piezoelectric actuator disposed in the holder body; the piezoelectric actuator has elements, stacked one above the other between an actuator head and an actuator foot, and each of the elements have piezoelectric layers enclosed by inner electrodes. The elements are constructed, using a material with a suitable crystalline structure (piezoelectric ceramic) for the piezoelectric layers, in such a way that upon application of an external voltage to the inner electrodes, a mechanical reaction of the elements ensues, which as a function of the crystalline structure and the regions of contact with the electrical voltage represents a compression or tension in a predeterminable direction. In a piezoelectric injector, the piezoelectric actuator is connected to a nozzle needle, so that by application of a voltage to the elements, a nozzle opening is uncovered.
In diesel piezoelectric injectors, in so-called direct nozzle needle control, the piezoelectric actuators operate directly in the diesel fuel at high pressure. For protecting the elements, for example with a view to insulating them electrically, it is known to sheathe the piezoelectric actuator with a diesel-proof elastomer. A disadvantage of this is that elastomers used for the purpose are not diffusion-proof to diesel fuel, water, and other media in the fuel.
From German Patent Disclosure DE 101 39 871 A1, a piezoelectric injector with an actuator module, acting on a valve member via a hydraulic pressure booster, is known in which the elements of the piezoelectric actuator are disposed in a sleeve provided with a corrugated bellows.